Sunday, 30 May 2010

The final part of the series on squamates consists of the snakes. There are many ways to categorise snakes: traditionally and colloquially this is between the venomous and non-venomous varieties. In reality, the distinction is not so clear cut. There's also constricting and non-constricting snakes, again fraught with the same difficulty.

Boas belong to the family Boidae, often considered a subfamily of the pythons of the Pythonidae. The majority of the snakes belong to the family Colubridae, usually known as rear-fanged snakes or colubrids - these are mostly non-venomous and non-constricting. Members of the Elapidae include the notoriously venomous cobras, taipans, coral snakes, and sea snakes. The Viperidae and Crotalidae (sometimes considered under the same family) include vipers and pit vipers, the latter group including the rattlesnakes. There are many other smaller families of snakes, none of which I have photos of (all photos below: order Squamata; class Sauropsida; phylum Chordata).

Formerly included in the genus Acrantophis, the Dumeril's boa is a ground-dwelling boid from Madagascar and the island of Reunion in the Indian Ocean. It is closely related to that other famous boa (I don't mean the feather variety), Boa constrictor, which has the same vernacular name as its scientific one. Boids are native to the Neotropics, that is Central and South America and the West Indies (with a few species in North America), as well as the Old World in parts of Europe, Africa, southern Asia and New Guinea.

There are many species of tree boa of the genus Corallus distributed in the Neotropics. The emerald tree boa is probably the most well known - the adult is green with white bands, while the young are a shocking orange or scarlet in colour. They bear a remarkable resemblance to the unrelated green tree python (see below), an excellent example of convergent evolution.

The green tree python is an arboreal python from Australia and New Guinea, green in its adult stage and red or maroon as a juvenile. The heat pits present in boids and pythons can be seen in the above photograph - these enable the snake to 'see' a thermal image of its warm-blooded prey. This extra sense makes up for the lack of hearing common to all snakes.

This is a beautifully-coloured morph of the coastal carpet python native to eastern Australia. Carpet pythons are closely related to green tree pythons, but are, as their name suggests, mostly terrestrial.

The reticulated python is a Southeast Asian snake which holds the record for the longest living snake, commonly exceeding 8.7 m (28 feet) in length. The green anaconda (Eunectes murinus) is often thought to hold that title, but although it is a bulkier and heavier animal, it rarely gets as long. Note the iridescence on the scales of this beautifully-patterned individual.

One of the more commonly kept large snakes belongs to the species Python molurus, but not to the nominate race (see below). The Indian python is less commonly seen in captivity - it is less boldly marked than the Burmese python.

It is the Burmese python that is a more common pet, with a more easterly distribution in the wild than P. m. molurus. They have become established in parts of southern Florida in recent years as ignorant former pet-owners release their unwanted serpents into the wild.

The ball, or royal, python is native to western and central Africa and is quite small for a python, making it the ideal pet for someone who wants a python but not a P. reticulatus or P. molurus! They habitually curl into tight balls in defence, giving them one of their common names.

A classic member of the Colubridae, a large group of rear-fanged snakes, very few of which are any danger to humans. It's not a commonly seen species in captivity, but is kept by a few people, some of whom report that its bite is venomous.

The name 'boomslang' is Dutch for 'tree snake'. It is a tree-dwelling snake, native to Africa, and is notorious as being the most venomous of the back-fanged snakes. It is often confused with the even more venomous green mambas (Dendrophis spp.) of the Elapidae.

One of the earliest colubrid snakes, Pachyophis woodwardi was described by Franz Nopcsa, the Hungarian palaeontologist who famously killed himself shortly after killing his lover. Pachyophis is believed to have been a marine snake, as it was found in Cenomanian (mid-Cretaceous) marine deposits in Bosnia & Herzegovina.

The black mamba is a deeply-feared and infamous snake throughout much of Africa. It's not black, as you can see, more of a pewter-grey, but it is the inside of its mouth which is apparently jet black. I haven't seen that for myself, and one would think that that would be the last fact you ever learn as the mouth clasps around some extremity or another. It is a fast animal for one without any legs, moving at a top speed of 20 km/h (12 mph).

This is quite a shocking animal - it is a bulky yet short viper with a huge head, huge eyes, and an unbelievably complex pattern on its body. The Gaboon viper is native to west Africa where it lies on the forest floor, blending in perfectly. You can see by the size of its cheeks that it must have a potent amount of venom in its glands, indeed, although it is docile and only bites when absolutely provoked, the venom is indeed very toxic, but not necessarily fatal.

The rattlesnakes are a specialised group of pit vipers endemic to the New World. They are notorious for the sound they make, produced by hollow scales at the end of the tail which are rattled in warning. The scales are added with each successive moult, indeed hatchling rattlers can't rattle! Rattlesnakes are cryptically coloured in order to prevent their prey, usually small desert rodents, from detecting their presence as they wait for such animals to come into reach (they are detected using heat pits, much like those of boids). However, if the snake senses the presence of a more malicious and less delicious threat, it will shake its tail in warning. Only when this warning fails will it strike, delivering a potent bite of venom.

Not all rattlers are found in deserts though. The neotropical rattlesnake (C. durissus) is distributed throughout much of South and Central America, including tropical forests, and there are species like the timber rattlesnake (C. horridus) and eastern diamondback rattlesnake (C. adamanteus) from temperate forests of eastern North America. The Aruba Island rattlesnake is often considered a subspecies of C. durissus, and is critically endangered, with less than 230 individuals estimated to survive in the wild on the island of Aruba off the coast of Venezuela.

Sunday, 23 May 2010

The last of the lizards, and a couple of mosasaurs, before I begin on the snakes. Families represented here are the Varanidae, Scincidae, and Mosasauridae (order Squamata; class Sauropsida; phylum Chordata).

Monitor lizards are a group of large to enormous Old World lizards, including the largest of them all - the Komodo dragon (Varanus komodoensis - see below). They are found in a variety of habitats, from the most arid deserts to lush tropical rainforests, and take to the trees and water as well as dry land. The mangrove monitor is a widely distributed species from southeast Asia, parts of Australia, and many islands of the western Pacific Ocean. Although the specific epithet is 'indicus', it does not range as far west as India - the name supposedly refers to the Indies, which was the generic name given to most of southeast Asia in colonial times. True to its vernacular, it does frequent mangrove forests, as well as inland freshwater bodies.

The water monitor (V. salvator) is a large and widely distributed monitor lizard from southeast Asia. Some of its more distinctive races, including V. s. cumingi, were recently split from it taxonomically, becoming species in their own right. This new species, known as the Philippine water monitor, originates from three of the larger Philippine islands, and is known for having more yellow markings than any other monitor.

Closely related to the mangrove monitor, and it has only recently been separated from it, the peach-throated monitor is native to New Guinea. It is indeed sympatric with the mangrove monitor, meaning that they both occur in the same region and habitat, suggesting that they are taxonomically distinct. Its throat is not always peach, ranging from white through to red.

The largest of the lizards, and one of the most familiar of the monitors, the Komodo dragon is restricted to a few tiny islands in Indonesia. Their huge size has been attributed to the phenomenon known as insular gigantism, whereby animals on islands become larger than their mainland counterparts, due to an available large predator niche which needs filling. The Komodo dragon is the only terrestrial predator on the islands in which it lives.

Juvenile Komodo dragonLondon ZooJune 2007

It was recently discovered that female Komodo dragons can reproduce without having mated. This virgin birth phenomenon is known as parthenogenesis, and until it was discovered in this species, it was previously only known in a few lizards and snakes. The other recent discovery concerning Komodo dragons is the verification that they are venomous - it has been known for a long time that they can bring down animals as large as fully grown water buffalo, but the mechanism involved was thought to be restricted to bacteria present in the lizard's mouth which cause infection. It is now known that they actively produce venom, albeit not in huge amounts, and it takes prey animals several days to die.

The Bosc's, or savannah, monitor is a fairly large terrestrial species from the savannahs of sub-Saharan Africa. It is smaller than the closely related rock monitor (V. albigularis) and the Nile monitor, with which the Bosc's monitor is sometimes confused.

One of the smallest monitor lizards, the emerald tree monitor is also one of the most striking in colour. There are many similar species under the same complex, grouped together as 'green tree monitors'. This species is restricted to the island of New Guinea, while others are found in surrounding areas.

Australia has a great variety of monitor lizards. Most of the mid-sized ones are colloquially called goannas, and the biggest of them all is the perentie (V. giganteus). The ridge-tailed monitor is a small species, never reaching more than around 60 cm (2').

Mosasaurs were a group of mostly very large marine lizards. They were closely related to the monitor lizards, and probably shared a common ancestor during the mid to late Mesozoic era. Plioplatecarpus lived in Laurasian seas, as fossils have been found in both North America and Europe - during the late Cretaceous, these two continents would have been very close together.

Skinks are a widespread family of lizards distributed in every continent but Antarctica. There are few species in Europe, many of them having reduced limbs. The ocellated skink is related to the three-toed skink (C. chalcides), which is one of those with very small vestigial limbs, and tiny toes.

The head of this reptile is on the right: the tail is used for defence by the skink as a decoy. Like other members of the genus Tiliqua, T. rugosa has a dark blue tongue which it flashes at potential threats. It is reputed to have the most vernacular names of any lizard, including bobtail skink, stump-tailed skink, bogeyes, pinecone lizard, and Australian sleepy lizard.

This is the only member of the genus Tiliqua not to be found in Australia - it originates from New Guinea. As its name suggests, it is larger than the other species, and does indeed have a blue tongue.

Anoles are a group of lizards related to iguanas, indeed they are sometimes placed within the same family. They are distributed in subtropical and tropical parts of the Americas, including most Caribbean islands. The brown anole is native to Cuba and the Bahamas, and has been introduced to the USA. I saw no other species of lizard in my two weeks in Florida in 2007 (except the other alien, see below), but brown anoles abound. The male, as can be seen in the top photo, flashes a colourful dewlap of skin at mates and rivals.

Spiny lizards are related to the horned toads - not toads, but they are somewhat reminiscent of those amphibians. I'm not sure if the spiny lizards can do this, but the horned toads are able to squirt blood from around their eye into the face of a potential predator, which is supposedly enough to deter most of them.

The fringe-toed lizards of the genus Acanthodactylus ('thorn finger') are distributed in arid habitats in parts of northern Africa, southern Europe, and southwest Asia. This species is found in Cyprus and adjacent parts of Turkey and the Near East. It is abundant, although it is classed as Endangered by the IUCN. Juveniles have bright red tails which fade as they mature; their striped bodies also fade. They aren't difficult to spot, but they are hard to approach. More pictures available on the ARKive website (submitted by myself!).

Although outwardly quite similar to the Schreiber's fringe-toed lizard, the snake-eyed lizard is less abundant, and just as shy. The eye is likened to that of a snake because it appears to lack eyelids, but they are really just clear and fused together, forming a protective 'spectacle'. As well as being found on Cyprus, it is distributed throughout much of the Middle and Near East, and as far east as India.

This species is endemic to Cyprus, but has close relatives in mainland Turkey and the Near East. It was until recently considered a member of the genus Lacerta, but this widespread genus has been broken down into several genera. The Troodos lizard bears similarities to the ocellated lizard (Timon lepidus) and green lizards (Lacerta spp.), and the male in the breeding season has a blue, green, and rufous coloration.

This is a critically endangered, medium-sized, tree-dwelling iguana endemic to the island of Utila off the coast of Honduras in Central America. Its tail has encircling bands of spines, hence the name.

There are many large species of iguanas found on islands: the marine iguana (Amblyrhynchus cristatus) is the only sea-dwelling lizard, and there are pink land iguanas on the Galapagos Islands, and blue ones in the Cayman Islands. The island of Hispaniola, shared between Haiti and the Dominican Republic, in the Caribbean Sea, is home to the rather large rhinoceros iguana. They are vulnerable to extinction, but thankfully are doing well in captive breeding programmes worldwide.

I spotted this individual in a tree while walking along the Anhinga Trail in the Everglades. I did not expect to see this. It is well known that stupid people set their pets free (I once did this, I am ashamed to admit... it too involved illegal aliens, American bullfrogs - Lithobates catesbeiana... oops!), so it should be no surprise that all sorts of exotic creatures can be found in the subtropical climes of the Everglades.

There are three species of iguana native to the islands of Fiji in the South Pacific Ocean, all of the genus Brachylophus. They are all severely threatened with extinction; one species, B. bulabula, was only described in 2008. The Fijian banded iguana differs from the similar crested iguana (B. vitiensis) by its shorter crest and bluer coloration.

There are two species in the family Helodermatidae - the Gila monster (H. suspectum - see below), and the Mexican beaded lizard. Both are notorious for being the only North American lizards with a venomous bite. They also share this beaded texture to their scales, giving this species its name.

The Gila (pronounced "hee-la") monster is not as monstrous as its name suggests. It is a placid animal and will only bite if provoked. Indeed, because it uses its venom to subdue and kill its prey, it will not waste it on stupid humans unless absolutely necessary. It has been discovered that certain compounds in the venom of Heloderma lizards have anti-diabetic properties - this is something which has earned the Gila monster and Mexican beaded lizard some good form of notoriety.

Geckos are another type of lizard familiar to most people - they are widespread in most warm parts of the world, some make excellent pets, and are reknowned for their ability to climb walls and ceilings with ease. The day geckos of the genus Phelsuma are found in Madagascar, so called because of their diurnal activity.

Most geckos have no true eyelids - the scales which form the eyelid have fused (see snake-eyed lizard above). The eublepharines are a subfamily of geckos which possess true eyelids. They also lack the adhesive pads on their toes. The leopard gecko is a very popular pet - it originates from arid and semi-arid regions of southern Asia.

Collared lizards are rarely seen in the pet trade, but are common in arid habitats in the west of the USA and Mexico. Males have the triple black collar on the neck which gives the species its vernacular and specific names. The colours become bolder and brighter during the breeding season.

Thursday, 20 May 2010

The order Squamata ('scaly ones') contains the lizards and snakes. The group used to be split into Sauria (the lizards) and Serpentes (the snakes), but this is not a natural grouping - snakes are legless, hypercarnivorous lizards. Since this is such a huge group (approaching 6000 species), with many interesting members, I shall break up the squamates into several arbitrary groups. The first contains the Agamidae, Anguidae, Chamaeleonidae, Cordylidae, and Corytophanidae (all order Squamata; class Sauropsida; phylum Chordata).

The lizard called the basilisk should not be confused with the beast of the same name famed in mythology, and another similar one from the world of Harry Potter. This creature is very much real, and can't kill its prey with a single stare. It does do one rather remarkable thing though: it can run on water on its hind limbs. I bet Nagini couldn't do that.

Plated lizards and sungazers are chunky, well-armoured African lizards of the family Cordylidae. They are popular pets, but not so popular as bearded dragons (see below). There are six species in the genus Gerrhosaurus, and this species can grow up to 69 cm in length.

Chameleons are a very well-known group of Old World lizards reknowned for many things: their eyes which can move independently of one another; their extremely long sticky tongue used to ensnare their invertebrate prey; and most famously, their ability to change colour. The panther chameleon is a large Madagascan species (the island has a huge diversity of chameleons, from the tiny leaf chameleons of the genus Brookesia to the Oustalets' chameleon - Furcifer oustaleti) with large spots on its body which change colour accordingly dependent on the animal's surroundings and mood.

There are two species of chameleon in Europe: this one occurs in Greece and many of the Aegean islands, as well as Cyprus and elsewhere. The African chameleon, C. africanus, also occurs in Greece. We spotted this individual crossing the road in the vicinity of Famagusta on the eastern coast of North Cyprus. I found it retreating into the undergrowth and attempted to catch it but it put up a fight, hissing and rocking its body from side to side as only pissed off chameleons know how to do. I had to make do with a few fuzzy photographs, and this one which captures its mood perfectly I think.

There are several families of legless lizards - many people in Britain and Europe are familiar with slow worms (Anguis fragilis), a legless lizard which is oft mistaken for a snake. The scheltopusik is a Eurasian species, also called the glass lizard. This name originates from the common behaviour strategy amongst many lizard groups to shed their tail when stressed - a phenomenon known as caudal autotomy. This is also the origin to the specific name of the slow worm - fragilis - something which many people realise when they pick up a lizard by the tail and are left with a wriggling tail and a look of shock on their face.

Uromastyx lizards, also called dab lizards, mastigures, or spiny-tailed lizards, are desert-dwelling reptiles from north Africa and the Middle East with fattened spiny tails. These tails are used as a fat source and a defence against would-be predators.

A large tree-dwelling agamid with two conspicuous sails on its back and tail, the Philippine sailfin lizard will escape predators by plunging into the water below the tree in which it will otherwise be resting. They are good swimmers and, like the basilisk, can run on water, but quadrupedally rather than bipedally.

One of the best known of the agamids, the frilled lizard or frilled dragon is familiar to most people for its threat display. The fold of skin which almost completely encircles its neck is erected, the mouth is opened, and the lizard runs on its hind legs towards its attacker. This is usually enough to deter its predators, which in the Australian outback would include dingos, monitor lizards, quolls, and birds of prey. The frill around the neck also features on the Dilophosaurus in the first Jurassic Park movie - there is no evidence for this, nor its ability to spit venom in the faces of dinosaur DNA thieves.

The family Agamidae is distributed in the Old World, with many species found in Africa, Asia, and Australasia. It is represented only by Laudakia stellio in Europe, and only marginally at that. It is one of the most common reptiles in Cyprus, and large and small individuals abound wherever there is a sunny spot to bask. It is also the largest lizard present on the island.

Juvenile agamaWild at Bellapais AbbeyOctober 2008

Young agamas are more brightly patterned than the adults, as the above individual shows. They commonly have a diamondback pattern and a banded tail.

The bearded dragon is probably everyone's favourite agamid... it certainly is a popular pet, and rightly so. It can be a charming, friendly, and inquisitive companion, isn't very demanding in its needs, and gets to a manageable size. Best of all, you can handle them - you can't do that to amphibians.

There are seven species in the genus Pogona, and most them do appear in the pet trade from time to time. Since they differ only in very small ways, it can be difficult to tell which species any given individual is. The majority probably belong to P. vitticeps (Ahl, 1926), the inland bearded dragon, which is the most common in the wild, although Lawson's dragons - P. henrylawsoni Wells & Wellington, 1985 - are popular too.

It has been observed that some species, including P. barbata, have vestigial venom glands from the ancestral squamate from which all lizards and snakes evolved. Not only is venom present in snakes, but also in two groups of lizards - the monitors and the beaded lizards - it could be found to be present in other lineages too. Of course, bearded dragons are completely safe to handle - the venom glands are not ducted and they do not have fangs.